Process for manufacturing macromolecular cellulose fiber



Patented Apr. 8, 1952 PROCESS FOR MANUFACTURING MACRO- MOLECULARCELLULOSE FIBER Shozo Tachikawa, Sanjo, Higashiyama-Ku,

Kyoto, Japan No Drawing. Application February 20.1950, Serial No.145,307. In Japan November 21, 1949 The present invention relates to aprocess for manufacturing low alkaline viscose of macrocellulosemolecules, consisting in obtaining low alkaline macro-molecularcellulose from cellulose material having initially a degree ofpolymerization (abbreviation-D. P. will be used hereinafter) above 800,by steeping same in a steeping solution, as low in caustic soda aspossible, in accordance with the D. P. of said cellulose material, underreduced pressure at the beginning of steeping and suitable higherpressure later, secondly obtaining macro-molecular low alkalinexanthogenate by pressing-down the cellulose thus obtained forcibly andthen by subjecting it to xanthation with suitable addition of carbonbisulphide, under suitable pressure regulated according to the D. P. ofsaid material cellulose, and thirdly dissolving xanthogenate thusobtained again in carbon bisulphide and water. The object of the presentinvention lies in manufacturing a low alkaline viscose consisting ofmacro-cellulose molecules-on a commercial scale, which is readilyspinnable in either an alkaline, neutral or 3% dilute sulphuric acidbath, from macro-molecular ,cellulose, as raw material, possessing D. P.above 800, for the purpose of manufacturing-the macromolecular rayonfiber with D. P. above 500, 'of high dryand wet-strength and of highdurability.

It is well known that, in manufacturing viscose-rayon fiber, a. lowcellulose, high alkali and low viscosity viscose is prepared frommaterial pulp-of around 700 D. P., by xanthating and dis-'- solving samein the usual way, under abolition of aging, which lowers the D. P. ofthe alkali cellulose most remarkably, and that the regenerated fiberobtainable from above viscose by spinning in an ordinary way possesses aD. P. below 400 and can display no characteristic peculiar to themacro-molecular structure.

Various processes have already been introduced for obtaining rayon fiberof fairly high D. P. from material of around 700 D. P., for instance.steeping raw material ina solution of ordinary or higher caustic sodaconcentration, pressingdown the steeped product to obtain alkali cellu-Qlose and xanthating the unaged cellulose with relatively. a largequantity of carbon bisulphide, or as an alternative procedure,xanthating above unaged cellulose under high pressure in an inert gas,or the like processes. I However, those processes are not satisfactoryfor such high D. P. cellulose material as above 800 D. P. In fact, evenin those processes, it is difficult to obtain such high D. P. rayonfiber as above 500 which.

3 Claims. (01. 1s- -54) possesses characteristic properties inherent inthe macro-molecular structure. It is an accepted fact that the higherthe D. P. of rayon fiber is, the more the properties of the finishedproduct can be improved. However, the regenerated fiber that can beobtained in the usual process, possesses a D. P. below 500, a value farbelow that of natural cotton fiber, and by no means satisfactory. Thisunfavorable result calls for a better process to obtain a product ofhigher D. P. I In the. present invention, raw material composed ofcellulose above 800 D. P., for instance, refined cotton linter or anyspecial pulp is used, in preventing the lowering of D. P. as much aspossible. Therefore, entirely new processes are adopted in each stage ofmanufacturing viscose: First, in the steeping with caustic soda, thecaustic soda concentration of the steeping solution is variedsubstantially inversely with the D. P. of cellulose material. Thesteeping is conducted at first under 'reducedpressure in order tomeet'the decrease in combined caustic soda due to the said dilution,thus facilitating the permeation of the steeping solution into thecellulose material quickly and uniformly, and simultaneously excludingoxygen occluded in the steeping solution as well as in the materialfiber, so that the lowering of the D. P. of cellulose that mightotherwise be caused by the decomposition due to oxidation duringandafter formation of falkali'cellulose, canbe suppressed. Q Thereafter,the formation of cellulose I is accelerated by the subsequent steepingunder appropriate pressure adjusted according to the concentration ofsteeping solution, thus enabling the formation of satisfactory alkalicellulose. In this case, an inert gas such as nitrogen without used ascompressing medium. Thus, the lowering of D. P. during the course ofsteeping has .been prevented by the following means: lowering of thecaustic soda concentration for the steeping solution; perfect possiblesuppression of oxygen effect, as well as shortening of steeping time.Then, it is needless to say that strong possible squeezing is necessaryfor removing free adsorbed alkali. The fundamental principle is toincrease the compressionand hence lower the press weight or ratio as thD. P. of alkali cellulose becomes higher, becausefthe rate of decreaseof D. P. of said cellulose due to the reaction of caustic soda is higheraccording as the D. P. becomes higher.

Shredding is conducted at low temperature in a short interval innitrogen atmosphere in order that low alkaline macro-molecular cellulosemay be obtained by checking the fall of D. P. of said alkali cellulose.

In the subsequent xanthation process, a fairly large quantity of carbonbisulphide (over 45% of the cellulose used) is added to unaged alkalicellulose.

The oxygen in the reaction apparatus which will otherwise effect thedecrease of D. P. during xanthation, is replaced beforehand withnitrogen while the apparatus is kept vacuum.

As described above, the' lowering of caustic soda concentration ofsteeping solution is effected in accordance with the D. P. of cellulosematerial. Therefore, it is inevitable that the xanthation will be themore difficult as the higher the D. P. of material cellulose is. Inorder to overcome the difficulty, the xanthation is carried out in aninert gas, under the pressure corresponding to D. P. of materialcellulose.

By means of this pressure, we can accelerate the xanthation as much aswe desire, without increasing the quantity of carbon bisulphidenecessary in order to overcome above difliculty in xanthation. So thedissolving procedure can be brought about very easily and favorably andeconomically.

Needless to say, it is necessary to control the quantity of carbonbisulphide, the reaction temperature and the pressure properly foruniform reaction and for preventing decrease of D. P.

One might consider simply that increase of carbon bisulphide, highreaction temperature as well as longer reaction time would be desirousfor getting favorable results when the alkali cellulose of high D. P.containing a small amount of free alkali is to be treated.

But in fact, such measures only cause a remarkable decrease in D. P.

In the present invention, those obstacles were surmounted by quick anduniform reaction effected in a short period of time under compression,thus allowing as little decrease of D. P. as possible and carrying out asatisfactory reaction.

The sodium xanthogenate cellulose obtained by the xanthation is notdissolved in alkaline water as in the usual process, but is dissolved ina mixture of water and carbon bisulphide. or by water and carbonbisulphide alternatively added, so that a viscose suitable to spinningis obtained.

As described above, free alkali being kept minimum and lowering of D. P.being controlled throughout the whole process. the D. P. of cellulose ofviscose obtained is extremely high and free alkali content is low.Therefore, the said viscose can be spun either in an alkaline, a neutralor less than 3% sulphuric acid bath, low in sodium sulphate. Inconsequence, macromolecular rayon fiber can be obtained having thecharacteristic properties peculiar to the macromolecular structure.

Following is the explanation of the present invention with regard to thepractical procedures. classified according to D. P. of cellulosematerial.

Case 1.Raw material: Refined cotton linter or special pulp of D. P.800-1000.

First, the cellulose material is steeped in an alkaline solution (16-17weight per cent caustic soda solution) for 20-30 minutes under less than60 mm. pressure. Next the reaction is con- 4 tinued for 30-60 minutesunder l-3 atmospheric pressure of inert gas, and it is then pressed downto 2.7-2.9 times the weight of cellulose and immediately shredded innitrogen atmosphere at as low temperatureand for as short a duration aspossible. Thus we obtain an alkali cellulose with sodiumhydroxide-cellulose ratio equal to 0.40-0.45. Without subjecting toaging, it is xanthated in a xanthating apparatus, and 45-55% carbonbisulphide is added.

In xanthation, the air in the reaction apparatus is previously replacedwith nitrogen gas and a desired quantity of carbon bisulphide is addedunder reduced pressure. After 30-60 minutes of operation when carbonbisulphide is adsorbed and hence the pressure is reduced, the pressureis raised up to 1-3 atmospheric pressure by introducing such inert gasas nitrogen and the reaction is continued for further -120 minutes.

Then at ordinary pressure, 5- of total dissolving water is sprayed intothe solution under agitation. After 20 minutes, carbon bisulphide, 5-10%of cellulose, is added, agitation is continued for further 30 minutesand the remaining dissolving water is added to complete dissolution.

The decrease in D. P. of the cellulose of the viscose thus prepared isvery slight and the content of free alkali is very little. A viscose of4-8% cellulose, 1.60-3.60% total alkali and 400-1,000 second viscositycan be obtained.

Case '2.--Raw cellulose material: D. P.:1,000- 1,200.

In case a cellulose of purified cotton linter of fairly higher D. P. issubjected to steeping with 17-18% sodium hydroxide solution, a quickdecrease in D. P. will take place in 10-20 minutes, thus resulting inthe formation of alkali cellulose of D. P. that is as low as thatobtained from raw material of lower D. P. The final product is not asatisfactory one.

When such a material as given for this case is used, it should besteeped in dilute alkali solution whose alkali content ranges from 15 to16% at the highest. For ensuring a quick and uniform reaction, first, itshould be steeped in 10-20 minutes under such a highly reduced pressureas less than 60 mm., and then after steeping in a fairly short durationunder a pressure, higher than that used in Case 1namely 4-10 atmosphericpressure, to complete the formation 0 perfect alkali cellulose.

In this case, the ratio of sodium hydroxide to cellulose in alkalicellulose is 0.37-0.40. It is pressed down to as heavy as 2.6-2.8 timesthe weight of cellulose and transferred to xanthation after shreddingsimilarly as in Case 1.

In xanthation, the air in the reaction apparatus is replaced withnitrogen gas similar as in Case inert gas as nitrogen as in Case 1.

Next, the xanthogenate is dissolved under agitation as in Case 1 orabove processes are repeated until all the sodium xanthogenate cellu-"lose. which is diflicult to diffuse, is completely dissolved.

The composition of the viscouse thus obtained is of 3-8% cellulose and1.10-3.20% total alkali,

with 5.00-1,500 second viscosity. 7

Case 3.Raw cellulose material:

With raw material of high D. P. as in this case, we meet with moredifficulty in each process, owing to inequality of minute structure ofraw material or ununiformity of distribution of its D. P.

From these reasons, we sometimes have to take the following procedures:

(a) When the process same as Case 1 is adopted, 11-15% sodium hydroxidesolution is used. steeping is carried out first for -20 minutes underless than 60 mm. pressure and then under 10-15 atmospheric pressure asin Cases 1 and 2. In this case, pressing down is taken as heavy as2.5-2.7 times the weight of cellulose.

(b) After steeping for such fairly short duration of time as 10-20minutes in ordinary concentration sodium hydroxide solution as 18%alkali content, the product is quickly pressed down and again steeped inalkali solution a little more diluted than in Case a, such as of 13-14%alkali concentration. Above manipulation we find makes the subsequentmanipulations easier, though the product gives the similar analyticalresults. I -i The ratio, sodium hydroxide: Cellulose in the alkalicellulose obtained in both (a) and (b) process was found to be0.34-0.37.

After this product was treated with carbon disulphide in a similar wayas in Case 2, it is treated under 6-10 atmospheric pressure, as in Cases1 and 2 .The composition of the viscose solution obtained in the aboveway was found to be of 2-6% cellulose, 0.68-2.22% total alkali, withGOO-3,000 second viscosity.

Case 4.Raw material: D. P.=higher than In this case, it is necessary touse Iii-14% alkali solution and 15 atmospheric pressure for our purpose.The conditions otherwise are followed just as in Cases 1, 2 and 3, whilethe pressing down is taken to be as heavy as 2.4-2.6 times the weight ofcellulose. The sodium hydroxide/cellulose of the alkali cellulose wasfound to be 0.30-0.34.

In this process, 2 stage steeping as in Case 3 (a) was found to beeffective as well.

In xanthation carbon disulphide of similar quantity as in the previouscase is used and under 12 atmospheric pressure, the whole process beingcarried out in similar way as in Cases 2 and 3.

The composition of the viscose obtained in the above way is of 1.5-6.0%cellulose and 0.4-2.00%

total alkali with over 800-3,500 second viscosity. Following are thepractical examples related in detail.

EXAMPLE I Linter pulp of D. P. of 870 is used as raw material.

After it is steeped in 16.5% sodium hydroxide solution at deg. C., thesteeping is continued for minutes under 100 mm. vacuumand then for morethan 60 minutes under 2 atmospheric pressure in nitrogen gas. I I .Afterbeing pressed down to as heavy as 2.8 timesthe weight of cellulose, itis shredded for 60 minutes at 15 deg. C.

The alkali cellulose thus obtained was found to be 33.5% of celluloseand 14.1% of total alkali. I Next,.without aging, it is directlysubjected to xanthation in an xanthation apparatus, where oxygen isexpelled previously under vacuum and filled with nitrogen gas, and thencarbon bisulphide (48% of cellulose) is added under reduced 75 Theregenerated cellulose has D.

pressure. After xanthation for 45 minutes at 25 deg. C. it is continuedfor further minutes under2 atmospheric pressure in nitrogen gas.

The produced sodium cellulose xanthogenate is dissolved at 15 deg. C. insuch way that first /is of the total dissolving water being sprayed,followed by 30 minute agitation, then carbon bisulphide (5% tocellulose) being added, followed by 30 minute agitation, the remainingwaterportion being added finally, with agitation kept throughout abovemanipulation, we obtain a product, viscose.

The composition of the viscose thus obtained is of 4.5% cellulose, 1.9%total alkali, sodium hydroxide ratio to cellulose=0.42, with 540 secondviscosity (time of dropping of a steel ball of 3 inch diameter 20cm. inone second) The regenerated cellulose was found to have D. P. of 550.

EXAMPLE 11 As raw material, refined cotton linter of D. P. of 1,120 wasused. It was steeped in 15.4% sodium hydroxide solution at 18 deg. C.for 20 minutes under 60 mm. vacuum and then for 60 minutes under 8atmospheric pressure in nitrogen gas. The product was pressed down asheavy as 2.7 times the weight of cellulose and shredded similarly as inExample 1. The constituents of the alkali cellulose were found to be36.4% cellulose and 13.5% total alkali.

This product was xanthated in reaction apparatus similar as used inCase 1. First the air in the apparatus was replaced with nitrogen gasand the product was xanthated under reduced pressure. Then carbonbisulphide (46% to cellu-- lose) was added, and after 60 minutes thereaction was continued for further minutes under 5 atmospheric pressurein nitrogen at 23 deg. C. The resolution was carried out as in Case 1.

The obtained viscose was found to be of 3.0% cellulose, 1.1% totalalkali, sodium hydroxide: ce1lulose=0.37 and 620 second viscosity.

The regenerated cellulose had D. P. of 720.

EXAMPLE III As raw material, refined cotton linter of D. P. of 1,350 wasused. It was steepedin 18% sodium hydroxide solution at 20 deg. C. for15 minutes. The product was pressed down as heavy as 2.8 times theweight of cellulose and again steeped in 14.2% sodium hydroxide solutionfor 20 minutes, under 20 mm. vacuum, and then for 60 minutes at 16deg.-C. under 12 atmosphericpressure. The product was pressed down. asheavy as 2.6 times the weight of cellulose and shredded similarly as inExample 2.

The constituents of the produced. alkali cellulose werefound to be of37.2% cellulose and 13.0% total alkali. This was xanthated similarly asin the previous example; with carbon bisulphide (50% to cellulose). for60 minutes at 23 deg. C. under 8 atmospheric pressure, and [is of totaldissolving water was added, followed by 30 minute agitation and thencarbon bisulphide (5% to cellulose) added, followed by 30 minuteagitation. The similar quantity of carbon bisulphide and waterrespectively were added by turn, the agitation still being continueduntil all the carbon bisulphide and water were added to make perfectviscose.

The produced viscose was found to be of 4% cellulose, 1.4% total alkali,sodium hydroxide: ce1lulose=0.35, and 950 second viscosity.

P. of 920.

7 EXAMPLE 1v As raw material, refined cotton linter of D. P. of 1,460was used. It was steeped in 13.2% sodium hydroxide solution for 20minutes at 15 deg. C. and 10 mm. vacuum and for 60 minutes underatmospheric pressure, and after pressed down as heavy as times theweight of cellulose treated as in the previous example. The producedalkali cellulose has 38.4% cellulose and 12.6% total alkali.

Carbon bisulphide (50% to cellulose) was added to this alkali celluloseand after xanthation and dissolution under 12 atmospheric pressuresimilar as in Example III, viscose is obtained.

The composition of the produced viscose is of 6.0% cellulose, 1.98%total alkali, sodium hydroxide: cellulose=0.33, with 2,000 second viscosity.

The regenerated cellulose has D. P. of 1,150.

Thus we have succeeded in producing a regenerated fiber of macrocellulose molecule of high degree of polymerization from such a lowalkali viscose of macro cellulose molecules obtained through eachprocess of the present invention, by spinning in a spinning bath,alkaline, neutral, or of dilute less than 3% sulphuric acid and of lowsalt content, less than 3% sodium sulphate.

It appears from the foregoing examples that in accordance with thisprocess, the alkali concentration and the pressure for steepingsolution, the degree of pressing-down for said alkali cellulose and themagnitude of pressure for Xanthation are adjusted in accordance with thedegree of polymerization of the raw material used as shown in thefollowing table:

remarkably high D. P. which shows vividly all the specialcharacteristics of macromolecular cellulose.

I claim:

. 1. In the manufacture of macromolecular cellulose fiber with D. P.above 500, the process consisting in steeping cellulose-containingmaterials having macromolecular cellulose of not less than 300 D. P. inan alkali bath the concentration of which varies inversely as the D. P.of the cellulose within the range of 17% for 800 D. P. to 13% for 1400D. P., pressing the alkali cellulose thus formed so that the ratio ofthe press weight of the material to the weight of the original cellulosevaries inversely with the D. P. of the cellulose within the ratios ofsubstantially 2.8 times the cellulose weight to 2.4 times the celluloseweight; shredding the unaged alkali cellulose thus obtained in anatmosphere of inert gas, xanthating the unaged shredded alkali celluloseby adding thereto a quantity of carbon bisulphide of not less than ofthe alkali cellulose in the presence of an inert gas at a pressurevarying directly as the D. P. of the cellulose within the range ofsubstantially 2 atmospheres for 800 D. P. to over 12 atmospheres for1400 D. P., and dissolving the sodium cellulose xanthogenate thusobtained in water.

2. The process as defined in claim 1 in which the first part of thesteeping is carried on under reduced pressure and the rest of thesteeping is carried on in an atmosphere of inert gas at a pressure whichvaries directly with the D. P. of the cellulose within a range ofsubstantially 2 atmospheres, for 800 D. P. to 15 atmospheres for 1400 D.P.

3. The process as defined in claim ltogether The relation between'D. P.of the raw cellulose material and that of the regenerated cellulose, thefinal product, is as follows:

Moreover, the viscose manufactured according to the new methods of thepresent invention has many excellent qualities: as the D. P. of theproduct increases, there is an increase of dryand wet-strength, ratio ofdryand wet strength, elastic property and durability and capability ofmanufacturing rayon fiber of macrocellulose molecules with highpractical value.

Speaking in brief, the present invention can prepare economically inpractice a. cellulose of D. P. oi cellulose material D. P. of product3004, 000 5004300 1, 000-1, 200 000-800 1, 200-1, 400 800%, 000 Higherthan 1,400 Higher than 1, 000

with'the additional step of regenerating the cellulose by spinning thedissolved sodium cellulose xanthogenate in a dilute acid bath having astrength not in excess oi 3 SEIOZO TACHIKAWA.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,968,463 Schur et al July 31.1934 2,076,596 Richter Apr. 13. 1937 2,106,111 Bayerl et a l. Jan. 18,1938 2,117,038 Richter May 10. 1938 2,521,450 Costa Sept. 5, 19502,542,285 Mitchell Feb. 20, 1951 FOREIGN PATENTS Number Country Date167,201 Great Britain Aug. 2, 1921

1. IN THE MANUFACTURE OF MACROMOLECULAR CELLULOSE FIBER WITH D.P. ABOVE500, THE PROCESS CONSISTING IN STEEPING CELLULOSE-CONTAINING MATERIALSHAVING MACROMOLECULAR CELLULOSE OF NOT LESS THAN 800 D.P. IN AN ALKALIBATH THE CONCENTRATION OF WHICH VARIES INVERSELY AS THE D.P. OF THECELLULOSE WITHIN THE RANGE OF 17% FOR 800 D.P. TO 13% FOR 1400 D.P.,PRESSING THE ALKALI CELLULOSE THUS FORMED SO THAT THE RATIO OF THE PRESSWEIGHT OF THE MATERIAL TO THE WEIGHT OF THE ORIGINAL CELLULOSE VARIESINVERSELY WITH THE D.P. OF THE CELLULOSE WITHIN THE RATIOS OFSUBSTANTIALLY 2.8 TIMES THE CELLULOSE WEIGHT TO 2.4 TIMES THE CELLULOSETHUS OBSHREDDING THE UNAGED ALKALI CELLULOSE THUS OBTAINED IN ANATMOSPHERE OF INERT GAS, XANTHATING THE UNAGED SHREDDED ALKALI CELLLOSEIN THE PRESENCE THERETO A QUANTITY OF CARBON BISULPHIDE TO NOT LESS THAN45% OF THE ALKALI CELLULOSE IN THE PRESENCE OF AN INERT GAS AT APRESSURE VARYING DIRECTLY AS THE D.P. OF THE CELLULOSE WITHIN THE RANGEOF SUBSTANTIALLY 2 ATMOSPHERES FOR 800 D.P. TO OVER 12 ATMOSPHERES FOR1400 D.P., AND DISSOLVING THE SODIUM CELLULOSE XANTHOGENATE THUSOBTAINED IN WATER.
 3. THE PROCESS AS DEFINED TO CLAIM 1 TOGETHER WITHTHE ADDITIONAL STEP OF REGENERATING THE CELLULOSE BY SPINNING THEDISSOLVED SODIUM CELLULOSE XANTHOGENATE IN A DILUTE ACID BATH HAVING ASTRENGTH NOT IN EXCESS OF 3%.